Lithium is considered one of the most important and discussed commodities in the recent years. Due to its utilization in lithium-ion batteries, which are used in a range of various energy storage systems, including e-scooters, electric cars and household batteries, lithium is becoming increasingly sought after. Australia is the worlds leading producer of lithium ore, which is predominantly mined from lithium-bearing pegmatites (Swain, 2017). The second most important producer of lithium is from lithium brines, which are mined from a regional termed the “Lithium Triangle”, a region in the Andes mountains that includes parts of Argentinia, Chile and Bolivia (Cabello, 2021). A salar is a salt flat, saline lake, or a salt-encrusted depression that is formed in the depocenter of a basin. In 2019, salars located throughout Chile produced 77000 tonnes of Li, which was equivalent to 23% of the world total production (Cabello, 2021). Of particular interest is Salar de Uyuni, located in Bolivia is the largest salar in the word, covering an area >10,000 square kilometres and is estimated to contain half of the worlds known resource of lithium (Ericksen et al., 1978).
Lithium Brine Deposit Model
A number of similar characteristics are common among producing lithium brine deposits. These characteristics are outlined by Munk et al (2016) and include: (1) arid climate; (2) closed basin containing a playa or salar; (3) geothermal and/or volcanic activity; (4) tectonically driven subsidence; (5) a lithium source; (6) a single or multiple suitable aquifers; (7) sufficient time to concentrate a brine. Climate is one of the most important factors as it allows salars to be developed in a closed-basin setting, it plays a factor in the concentration of Li in brines and it is essential for the concentration of Li in evaporation ponds for economic purposes (Munk et al., 2016). The formation model for lithium brines is relatively simple and is outlined here. First, lithium needs to exist within a nearby suitable source rock. In the Lithium Triangle, the source rocks are considered to be various metamorphic and sedimentary rocks of the Palaeozoic basement and Cenozoic volcanics, especially the large intermediate and silicic ignimbrite rocks (Meixner et al., 2020; Sarchi et al., 2023). Secondly, the lithium needs to be leached from the various source rocks. This can occur through multiple processes including surface weathering of the source rock, or through the introduction of a relatively low-temperature geothermal fluid which propagates through faults (Munk et al., 2016). In addition, the concentration of Li in the brines may be increased via the recycling of Li-rich clays or through the remobilization of buried Li-rich salts (Godfrey and Álvarez-Amado, 2020; Marazuela et al., 2020). As lithium is highly soluble, unlike sodium (Na), potassium (K), or calcium (Ca), it does not readily produce evaporite minerals (Bradley et al., 2013; Munk et al., 2016). Over time, the lithium released from the various extraction processes mentioned above is preferentially concentrated in sub-surface brine bodies (Bradley et al., 2013; Munk et al., 2016). Li concentrations in economic brines range from 200 to 4,000 milligrams per litre (Bradley et al., 2013).
Extraction and Processing of the Brines
The sub-surface lithium brines are pumped from their aquifers using extraction wells. Upon extraction, the brine is diverted to large and shallow open-air evaporation ponds (Bustos-Gallardo et al., 2021; Cabello, 2021). A two-step process is often utilised where the brine is poured into a first set of ponds between 6-9 months in order for adequate evaporation for the removal of potassium chloride (Bustos-Gallardo et al., 2021). These brines are then pumped into a second set of pools for another 4-5 months, allowing Li (in the form of LiCl) to reach concentrations of approximately 6% while other elements including Na, K, & Mg precipitate out into various mineral phases such as halite, sylvanite, sodium chloride, and carnallite (Bustos-Gallardo et al., 2021; Cabello, 2021). In some instances, any remaining brine may be re-injected into the salar (Bustos-Gallardo et al., 2021). The concentrated Li brine is then transported to chemical processing plants where it is converted to lithium carbonate, lithium hydroxide or lithium chloride.
Conclusion
Lithium is a vital commodity for the production of lithium-ion batteries which are being increasingly used in various technologies. While Australia leads in lithium ore production, the "Lithium Triangle" in South America is the second-largest producer of lithium. Although the article presented this week is short and contains relatively few specific details, its primary aim is to familiarise the audience with the concept of lithium brine deposits, which make up almost half of the worlds lithium production. The formation model involves the leaching of lithium from a source rock, where it is eventually concentrated in sub-surface brine bodies. Extraction of lithium involves pumping the brines into various evaporation ponds for a select period of time, followed by additional offsite chemical processing.
References:
Bradley, D.C., Munk, L., Jochens, H., Hynek, S., Labay, K., 2013. A preliminary deposit model for lithium brines. US Department of the Interior, US Geological Survey Reston, VA, USA.
Bustos-Gallardo, B., Bridge, G., Prieto, M., 2021. Harvesting Lithium: water, brine and the industrial dynamics of production in the Salar de Atacama. Geoforum 119, 177–189.
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